Once had three stamps on one visa. When departing Dalaman the last time within the 90 days, one of the stamps had partly covered the date on the original entry stamp. You could see the "stamp" guy thinking he had a live "catch" and was quite chuffed with himself. He called over another guy, who then called over another, took about half an hour, but they finally agreed (with a Tut) I was still in the 90 day visa restriction.
This link will help you determine your visa expiry date;
http://www.timeanddate.com/date/dateadd.htmlK
